Current planar radiating element technology using high dielectric constant FR-4 materials cannot provide a radiating element with relatively wide frequency band and scan volume and good polarization performance. Conventional aperture coupled patch antennas have gain and polarization limitations. Electronically scanned antenna systems often employ a circularly polarized field. Linear polarization imposes inherent limitations on Active Electronically Scanned Antenna (AESA) systems. A circularly polarized radiating element with relatively wide frequency band and scan volume comprised of FR-4 material, would be preferable, if it could be achieved in a single unit cell.
Electronically scanned antennas generally include a manifold layer for distributing power to a feed layer. The feed layer feeds power to a patch layer that transitions the power to free space. The patch layer, for a conventional aperture coupled patch antenna, typically requires low dielectric constant materials that are unsuitable for FR-4 manufacturing processes. Further, the patch layer is substantially thicker than the manifold or feed layers, creating an unbalanced printed circuit board.
Aperture coupled patch antennas generally have a low dielectric constant substrate and two printed circuit board patches. Patches tend to scatter into lower order Floquet modes. In order for the patch to operate effectively, the lower order Floquet modes must be relatively constant over scan and frequency necessitating a small unit cell size and a low dielectric constant polytetrafluoroethylene (PTFE) based substrate. The small unit cell size means that the module density is high, significantly increasing the cost of the antenna and the thermal cooling requirements of the antenna. The use of low dielectric constant PTFE based material also significantly increases the cost of the antenna. Further, scan performance in the H plane scan is poor. Current planar radiating element technology cannot provide a low cost relatively broadband (˜30%) aperture coupled dual polarized radiating element comprised exclusively of FR-4 materials, manufactured using standard printed circuit board (PCB) processes, and with a built in radome. Furthermore, the PTFE based aperture layers are substantially thicker than the manifold or feed layers creating an unbalanced printed circuit board.
Consequently, it would be advantageous if an apparatus existed that is a balanced FR-4 printed circuit board, and suitable for use as an aperture coupled dual polarized radiating element with moderately wide frequency bandwidth and scan volume.